Aluminum for some time has been alloyed with various amounts of silicon. Based on the percentage content of silicon, the alloy can be characterized as a hypereutectic or hypoeutectic alloy. A hypoeutectic mixture is one which contains more aluminum than aluminum silicon eutectics. A hypereutectic alloy is therefore one which has more silicon than aluminum silicon eutectic.
The hypereutectic alloy is saturated with silicon thus having excess free silicon. Frequently magnesium is added to such hypoeutectic as well as hypereutectic alloys. For example, Goetzel U.S. Pat. No. 2,155,651 and Hall U.S. Pat. No. 1,871,607 both disclose hypoeutectic aluminum silicon magnesium alloys. Hypereutectic aluminum silicon alloys are disclosed, for example, in Hasegawa et al U.S. Pat. No. 3,841,919, Rasmussen U.S. Pat. No. 3,953,202 and Sterner-Rainer U.S. Pat. No. 1,940,922 which discloses an aluminum silicon magnesium alloy which has 5-40% silicon. A silicon content of 5-40% includes hypoeutectics and hypereutectics.
Phosphorus has also been added to hypereutectic aluminum silicon alloys. Its use is disclosed in the Sterner-Rainer reference. Further, Noguchi U.S. Pat. No. 4,147,074 discloses the addition of phosphorus to hypereutectic aluminum silicon alloys, but indicates that phosphorus is not required where the alloy contains less than 14% silicon. On the other hand, Desre U.S. Pat. No. 3,762,660 teaches the need to dephosphorize aluminum.